A red pigment is used in various fields such as cosmetics, paint for automobiles, general paints, plastics, ink, synthetic leather, prints, sundries, furnitures, ornaments, and fabrics.
There are many conventional red pigments which contain a red organic substance, such as carmine. However, conventional red pigments have various negative qualities, such as discoloring of organic substances, and further are unsafe for the human body.
On the other hand, a red pigment containing a red iron oxide as an inorganic red pigment is well-known. Examples of red pigments which are composed of inorganic substances are lamella mica particles in which a surface is coated with the red iron oxide, a titanium dioxide coated mica particle in which the iron oxide is further coated, and plate-type red iron oxide.
An inorganic red pigment composed of a red iron oxide has various merits, such as being safe and sunproof. However, the red pigment composed of the aforementioned red iron oxide is limited from a red color to a brown-red color, which is the color of the iron oxide itself. Also, the conventional inorganic red pigments do not have the various red-like hues, like organic pigments.
It is, however, possible to change the color tone of a pigment, e.g. by coating the surface of the mica particle with the red iron oxide and inorganic substances which have other color tones. In this case, the mixture of the material of more than one substance must be coated on the surface of the mica particle. However, this type of coating treatment is difficult to achieve since the mixture of the substances causes a problem in that the hues gradually become black because each material absorbs light and the lightness of the pigment notably declines.